Cloning, expression, purification, crystallization and X-ray crystallographic analysis of β-ketothiolase B from Ralstonia eutropha H16

Polyhydroxyalkanoates are linear polyesters that are produced by bacterial fermentation and are used as biodegradable bioplastics. β-Ketothiolase B (BktB) from Ralstonia eutropha (ReBktB) is a key enzyme for the production of various types of copolymers by catalyzing the condensation reactions of acetyl-CoA with propionyl-CoA and butyryl-CoA. The ReBktB protein was crystallized using the hanging-drop vapour-diffusion method in the presence of 25% polyethylene glycol 3350, 0.1 M bis-tris pH 6.5, 0.2 M lithium sulfate at 295 K. X-ray diffraction data were collected to a maximum resolution of 2.3 Å on a synchrotron beamline. The crystal belonged to space group C222₁, with unit-cell parameters a = 106.95, b = 107.24, c = 144.14 Å. With two molecules per asymmetric unit, the crystal volume per unit protein weight (V_M) is 2.54 ų Da⁻¹, which corresponds to a solvent content of approximately 51.5%. The structure was solved by the molecular-replacement method and refinement of the structure is in progress.